The present invention concerns the technical field of antenna arrangements.
Conventionally, an antenna arrangement including an antenna, a receiver and a transmitter, able to couple the antenna alternately to the transmitter (in transmission phase) and to the receiver (in reception phase), is used.
One problem encountered in such an antenna arrangement is achieving an optimum coupling between the transmitter and the antenna.
With reference to FIG. 1A of the present description, GB Patent No. 2,323,799 of Motorola Israel discloses an antenna arrangement 10 including an antenna A, a transmitter (the latter including at its output a power amplifier 16), and means 18 for coupling antenna A and the transmitter.
Coupling means 18 are formed by a transmission line able to transform the output impedance of amplifier 16, as is described in more detail hereinafter. It will be noted that line 18 operates like a phase lag circuit.
It is to be noted that line 18 allows the transmitter to be isolated from antenna A, in the event that the latter is not in transmission phase (in particular in reception phase). In such case, power amplifier 16 is controlled so as to no longer provide a signal, and its output impedance is then of a highly reactive nature. Line 18 is thus arranged so that the impedance seen from antenna A to the transmitter corresponds to that of an open circuit (high impedance). In other words, the transmitter is insulated from antenna A, and a radiofrequency signal received by antenna A is provided to the receiver.
One drawback of the arrangement of antenna 10 is that it includes transmission lines, which involves a considerable space requirement for this arrangement.
Another drawback of the arrangement of antenna 10 is that it requires making an additional circuit able to control power amplifier 16, which is counter to the usual industrial concerns as to limiting space requirement, weight, electric power consumption and thus the cost of manufacturing and use.
With reference to FIG. 1B of the present description, the document  less than  less than Drain supply switching of mobile phone power amps with pulsed operation mode greater than  greater than , Siemens Application Note No. 009, Discrete and RF semiconductor division, Edition A03, describes a control circuit 23 including control means 25 and a field effect transistor 28 (of P type channel). Transistor 28 is connected between a supply terminal (for receiving supply voltage Vb) and the system""s earth, via supply terminals of power amplifier 16. Transistor 28 is controlled by control means 25 so that, when antenna A is in transmission phase, amplifier 16 can provided a sufficiently powerful radiofrequency signal (RF) from the transmitter to antenna A, with a minimum of electric power loss.
Moreover, the Applicant of the present invention has observed that, when antenna A is in transmission phase, the provision of the radiofrequency signal is not optimum, from the point of view of electric power losses, and that, when antenna A is not in transmission phase, the isolation of the transmitter and antenna A is not optimum, since the output impedance of amplifier 16 can vary.
One object of the present invention is to provide an antenna arrangement including an antenna and a transmitter, this arrangement overcoming the aforementioned drawbacks, to provide optimum coupling between the transmitter and the antenna, i.e. coupling causing a minimum of electric power losses RF.
Another object of the present invention is to provide an antenna arrangement able to provide control of the power amplifier of the transmitter, without resorting to additional components (for example a field effect transistor of P type channel).
Another object of the present invention is to provide an antenna arrangement answering the criteria of minimum complexity, low power consumption, compactness and low cost, which are conventional in telecommunications.
These objects, in addition to others, are achieved by the antenna arrangement according to claim 1.